Antenna system



March 8, 1938. J. A. POOL 2,110,715

ANTENNA SYSTEM Filed March 28, 1936 RECEI VER as I J ZSnventor Ohm .1 OZ

Patented Mar. 8, 1938 UNITED STATES ANTENNA SYSTEM John A. Pool, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 28, 1936, Serial No. 71,377

6 Claims.

This invention relates to antenna systems and particularly to antenna systems which have directive properties. It is well known that horizontal antennas of the order of a half wave length have directive patterns. If a horizontal antenna is erected in a position pointing north and south, the field set up by energizing the antenna will be most intense in an east-west direction. This field pattern is normally of a figure 8 shape.

If such an antenna is rotated 90 in a horizontal plane, the directive pattern will likewise rotate 90. The directive antenna increases the transmission range in the desired direction at the expense of decreasing the range in other directions. While in many installationsthe directive antennas are useful, their utility could be greatly increased if such directive properties could be readily and quickly altered without 20 physically rotating the antenna.

One of the objects of my invention is in the arrangement of an antenna system which has directive propertieswhich may be altered without physically rotating the antenna.

Another object is to transmit energy to the antenna through a symmetrically arranged transmission line so that several antenna combinations may be selectively employed without unbalancing the antenna or detuning the transmitter.

A further object is to symmetrically arrange the transmission line so that several combinations of antenna may be used without the transmission lineseffecting the directive properties of such combinations.

The invention may be best understood from the following description taken in connection with the drawing, in which:

Figure I represents an antenna system which is directive toward the east and west.

Fig. II represents an antenna system which is directive north'and south,

Fig. III represents an antenna system in which the antennas of Figs. I and II are combined to be directive in a northwest and southeast bear- Fig. IV is a schematic circuit diagram of one embodiment of my invention, and

Fig. V is a schematic circuit diagram of another embodiment of the antenna system of Fig. IV including a filter network.

Referring to Fig.1.. a pair of horizontally arranged antennas I, 3, of preferably one-half wave length, are disposed in 90 relation. The antennas l, 3, are respectively connected to transmission line conductors 5, 1. A third conductor 9 is symmetrically disposed with respect to the other conductors 5, 1. The three symmetrically disposed conductors 5, 1, 9, are preferably rigidly supported by suitable insulators at the junction of the sides of an equilateral tri-. angle. The three conductors 5, l, 9 terminate in switch contacts II, I 3, l5. The outer pair of switch points II, 15 are connected by switc'h arms I! and I9 to the terminals of a tuned tank circuit 2]. This; tuned circuit is composed of an inductor 23 and a capacitor 25. The tuned tank circuit 2| is resonant to currents of the frequency to be. transmitted or received and is coupled to a suitable transmitter, receiver, or suitable terminal apparatus.

The operation of the antenna system of Fig. I is essentially as follows: The tuned tank circuit is connected to the transmission line conductors 5, 9. Energy from the tank circuit 2| is fed in opposite phase through these conductors 5, 9. Since the antenna l is directly connected to the conductor 5, energy will be fed to this antenna, and radiated therefrom in the conventional manner. The field pattern will be a figure 8 as represented by the circular lines 21, 29. The second horizontal antenna 3, connected to conductor 1, will receive no energy from the transmission line composed of the conductors 5, 9- because the conductor l to which this antenna 3 is connected is symmetrically positioned or neutrally coupled with respect to the other conductors 5, 9. In this position currents induced in the conductor 1 by the energy flowing in conductors 5, 9 will be equal and opposite and therefore balanced out. The coupling between the antennas, I, 3 will be slight and I have found that its effect is negligible.

In Fig. II the tank circuit 2| is connected to the pair of conductors 1, 9; one of these conductors 1 is connected to the antenna 3. The energy flowing from the tank circuit 2i energizes the connected conductors 1, 9 and antenna 3 but the antenna I being connected to the symmetrically positioned or neutrally coupled conductor 5 is not energized as previously described. The resulting radiation has a field pattern represented by the circular lines 3|, 33.

In Fig. III, the tank circuit; 2! is connected to the pair of conductors 5, 1. Both of these conductors are respectively connected to antennas l 3. The third conductor 9 is symmetrically arranged with respect to the pair of conductors 5, 1, has no efiect on the system, and no currents are induced in it by energy flowing in the pairs of conductors 5, I. Since both antennas l, 3 are energized radiation therefrom will have a re sultant figure 8 field pattern 35, which lies intermediate the field patterns of Figs. I and II.

In Fig. IV the tuned tank circuit 2! is coupled to the transmitter or receiver 39 through a coupling inductor 4| or other suitable means. I prefer to first erect the symmetrically arranged transmission line conductors 5, I, 9 which are of equal length and tune the pairs of the several combinations; namely 5-1, 5-9, and 1-9 so that each set of pairs has exactly the same resonance characteristic and will therefore not detune or unbalance. the network as they are successively connected by the switches ll-l9 If the antennas I, 3 are resonant to exactly one half of the wave length to be transmitted, they may be connected Without affecting the tuning of the transmission network. Thereafter the several antenna combinations represented by Figs. I, II, and III may be selectively employed to obtain the required directive characteristic.

Instead of first tuning the transmission network 5, l, 9 and 2| as previously described with antennas l, 3 disconnected, the antennas may be made of the approximate length required and connected to the conductors 5, l. The complete antenna structure may then be tuned to resonance. If the antenna lengths, the conductor lengths and symmetry have been carefully established, the several antenna arrangements may be employed without detuning the transmitter, or aiIecting the several directive patterns. In Fig. V a filter network 43 has been substituted for the single tuned tank circuit 2!. In other respects, the circuit of Figs. IV and V are similar.

By way of example, -I have found that the transmission line conductor spacing may be of the order of 19 centimeters, and the antenna lengths 20 meters for an effective wave length of meters. The antenna system may be aligned with respect to the compass points to establish the desired directive effects. Likewise, the angle between the antennas or between the antennas and earth may be varied to establish other field patterns. The antenna portions may be used to establish vertical or horizontal polarization of the radiated energy.

It should be understood that my invention applies equally well to receiving or transmitting radio frequency energy. The symmetrical arrangement of each of the transmission line conductors, not only permits the simple switching arrangement whereby the several directive antenna characteristics may be selected, but also prevents distortion of the directive pattern by the cancellation of radiation from the transmission line conductors themselves.

I claim as: my invention:

1. An antenna system comprising a pair of angularly disposed antennas, a three-conductor transmission line, said conductors being positioned substantially at the corners of an equilateral triangle, a connection from one of said antennas to one of said conductors, a connection from the other of said antennas to another of said conductors, terminal apparatus, and means for selectively connecting said conductors in pairs to said terminal apparatus.

2. An antenna system comprising a pair of antennas disposed in 90 relationship, a threeconductor transmission line, said conductors being equally spaced from each other, a connection from one of said pair of antennas to one of said conductors, a connection from the other of said pair of antennas to another of said conductors, terminal apparatus, and means for selectively connecting said conductors in pairs to said terminal apparatus.

3. An antenna system comprising a pair of half wave horizontal antennas disposed in angular relationship, a three-conductor transmission line, said conductors being substantially equally spaced from each other, a connection from one of said antennas to one of said conductors, a connection from the other of said antennas to another of said conductors, terminal apparatus, and means for selectively connecting said conductors in pairs to said terminal apparatus.

4. An antenna system comprising two half wave horizontal antennas disposed at 90, a three-conductor transmission line, said conductors being positioned substantially at the corners of an equilateral triangle and angularly disposed with respect to said antennas, a connection from one of said antennas to one of said conductors, a connection from the other of said antennas to another of said conductors, terminal apparatus, and means for selectively connecting pairs of said conductors to said terminal apparatus.

5. An antenna system comprising two half wave horizontal antennas disposed at 90, 2. three-conductor transmission line, said conductors being substantially equally spaced from each other and angularly disposed with. respect to said antennas, a connection from one of said antennas to one of said conductors, a connection from the other of said antennas to another of said conductors, a transmitter for generating radio frequency oscillations, coupling means between said transmitter and selected pairs of said conductors.

6. An antenna system comprising two half wave horizontal antennas disposed at 90, a three-conductor transmission line, said conductors being substantially equally spaced from each other and angularly disposed with respect to said antennas, a connection from one of said antennas tonne of said conductors, a connection from the other of said antennas to another of said conductors, a transmitter for generating radio frequency currents, means for selectively connecting pairs of said conductors to a tunable tank circuit, and means coupling said transmitter and said tunable tank circuit.

JOHN A. POOL. 

